N-nitroso-4,4&#39;-bis(2-phenylisopropyl)-diphenylamine

ABSTRACT

N-NITROSO-4,4&#39;&#39;-BIS(2-PHENYLISOPROPYL) DIPHENYLAMINE, A NEW COMPOUND, IS VALUABLE AS A VULCANISATION RETARDER FOR ELASTOMERS. IT HAS AN ANTI-AGEING EFFECT ON THE VULCANISED PRODUCT.

United States Patent Int. Cl. sbsr 45/60 US. Cl. 260-453 4 ClaimsABSTRACT OF THE DISCLOSURE'N-nitroso-4,4-bis(Z-phenylisopropyl)diphenylamine, a new compound, isvaluable as a vulcanisation retarder for elastomers. It has ananti-ageing efiect on the vulcanised product.

The present invention provides a new compound which is useful as aretarder of the vulcanisation of natural and synthetic rubbers and whichfurthermore possesses valuable properties of protection againstdeterioration due to the ageing of vulcanised articles.

It is well known that during the various stages of using a mixture basedon rubber and containing the ingredients required for vulcanisation, inparticular sulphur and vulcanisation accelerators, prolonged heatingstake place which can lead to premature vulcanisation. Suchprevulcanisations make the mixtures unsuitable for their subsequentconversion.

The risks of pre-vulcanisation may be reduced by using a retarded-actionacceleration such as, for example, an accelerator of the sulphenamideclass and/or by adding to the composition a vulcanisation retarder, alsocalled an anti-scorching agent. The effect of such a vulcanisationretarder must be limited to the stage of using the mixture only and mustcease during the vulcanisation at 'a higher temperature so as not toincrease the duration of cure of the mixtures.

It is also well known that vulcanised rubber over the course of timeundergoes considerable degradation which is, in particular, due to theaction of oxygen and heat as well as to the particular conditions of useof the finished article. It is accordingly desirable to protectvulcanised rubber against the destructive effect of these variousfactors.

Up to now numerous products are known which can be used to combat therisks of scorching of raw mixtures, for example organic anhydrides andacids such as phthalic anhydride, salicylic acid, and nitroso-aminederivatives such as nitrosodiphenylamine. All these products areeffective under certain conditions, but they are not always completelysatisfactory because the former, the organic anhydrides and acids, donot completely have the desired effect on accelerators of thesulphenamide class, while nitrosodiphenylamine strongly colours thevulcanisation mixtures, so that the latter mixtures can mark lacquersand paints by contact.

Very many chemical substances are also known which may be used toprotect vulcanised rubber articles against ageing.

The present invention provides a new compound which simultaneouslypossesses both valuable retarder proper- 3,573,252 Patented Mar. 30,1971 ice ties, and also the protective properties which areindispensable for good preservation of vulcanised rubber articles. Thisnew compound is N-nitroso-4,4'-bis-(2- phenylisopropyl)-diphenylamine.This new compound has the formula:

Its melting point is 0., its absorption maximum at 298 m lia and itsabsorption minimum at 275 m lZmf 124 This compound is a very etfectiveretarder for counteracting the scorching of mixtures based on naturalrubber or on synthetic unsaturated elastomers such as styrenebutadieneand butadiene-acrylonitrile copolymers, polybutadiene, polyisoprene, andgenerally all unsaturated elastomers which can be vulcanised withsulphur. N- nitroso-4,4'-bis(Z-phenylisopropyl)-diphenylamine is used inan amount generally from 0.1 to 5 parts by weight (preferably 0.25 to 2parts) per 100 parts by weight of the unsaturated elastomer.

N nitroso 4,4'-bis(2-phenylisopropyl)-diphenylamine does notsignificantly interfere with the vulcanisation proper either from thepoint of view of speed or from the point of view of the properties ofthe vulcanised product. The new compound also makes it possible toprepare vulcanised rubber articles of much retarded degradation, and ithas the additional advantage, namely that it causes considerably lesssevere marking of lacquers and paints than that caused byN-nitrosodiphenylamine.

The product of the invention may be prepared from4,4'-bis(2-phenylisopropyl)-dipheny1amine by any process of introducingthe nitroso group. It is, for example, possible to disperse4,4'-bis(2-phenylisopropyl)-diphenylamine in water at a suitabletemperature (for instance at about 90 C.) and add a sufiicient quantityof sodium nitrite and a strong inorganic acid, such as for examplehydrochloric acid or sulphuric acid, to carry out the introduction ofthe nitroso group, and to separate the resulting product in any desiredmanner, such as for example by filtration after cooling or bydecantation of the liquids organic layer.

The use of the new compound of the invention in mixtures based on rubberis illustrated in the following examples:

EXAMPLE 1 This example shows the influence of the concentration of Nnitroso-4,4-bis(Z-phenylisopropyl)-diphenylamine on scorching in amixture based on natural rubber filled with carbon black.

The following mixture is prepared in a laboratory interrial mixer:

The following ingredients are added to the above mixture on a roll mill:

Parts by weight Sulphur 2.25 N-cyclohexylbenzothiazylsulphenamide 0.50

N nitroso 4,4 bis(2-phenylisopropyl)-diphenylamine (as indicated below).

After being left for 24 hours, the scorching time of the mixtures ismeasured on a consistometer of the Mooney function of the duration ofthe vulcanisation.

The results obtained are shown in Table I.

TABLE I N-nitrosobis(2-phenylisopropybdiphenylamine (parts by weight)Properties measured 0 0. 5O 1. O0

scorching time (min.) at

120 C 22. 5 25. 00 28. 75 130 C 13. 5 14. 75 16. Vulcauisation at 1430., tear resistance (kg./em. after- 25 20 minutes 246 245 233 25 minutes246 248 243 minutes 246 248 249 Modulus at 800% (kg/0111. after-- 0minutes 110 110 104 25 minutes--- 116 118 113 30 miuu 120 123 117 30Elongation at break (percent) after 20 minutes 550 535 535 25 minutes..-535 535 530 30 minutes 510 510 530 These results show thatN-nitroSo-4,4-bis(2-phenyl- 3 0 isopropyl)diphenylamine increases thescorching time with practically no modification of properties of thevulcanised articles.

If the N-cyclohexylbenzothiazylsulphenamide in the After being left for24 hours, the scorching time of the mixtures is measured on aconsistometer of the Mooney type at 120 C. Furthermore the mixtures arevulcanised in a press at 153 C. and the properties obtained at theoptimum vulcanisation time (the shortest 'vulcanisation time producingthe highest modulus at 500%) are measured.

Finally, the raw mixtures are stored for 15 days at ambient temperatureand their scorching time at 120 C. isagain measured.

The results are given in Table II below.

TABLE II N-nitroso4,4-bis(2-phenylisopropyl) diphenylamine (parts byweight) Properties measured 0 0. 5 1

Scorehing time at 120 0.:

After preparation of the mixtures- 9 14. 15. 50

After storage for 15 days 7 22. 50 28. 50 Vuleanisation at 153 0.:

Optimum time (minutes) 15 15 15 Tear strength (kg. /em. 98 102 103Modulus at 500% (kgJemfl) 28 29 30 Elongation at break (percen 750 765760 Shore A hardness 54 54 54 EXAMPLE 3 This example shows theprotective properties of N- nitroso-4,4'-bis 2-phenylisopropyl)diphenylamine against heat ageing of vulcanised mixtures.

Mixtures, which are vulcanised at 145 C. for the optimum time areprepared as in Example 1. The vulcanised articles obtained areintroduced, as samples, into a circulating air oven at 80 C. and thechange in strength and elongation at break are measured. The timerequired to achieve a certain reduction of the properties measured isthen determined. Mixtures were also prepared as in Example 1 butreplacing the N-nitroso-4,4'-bis(2-phenylisopropyl)-diphenylamine byN-nitrosodiphenylamine.

The results obtained are shown in Table III.

TABLE III N-nitroso-4,4-bis (2-pheny1-N-nitrosodiisopropyl)-diphenylamine phenylamine (parts by weight) (partsby weight) Time required to achieve a reduction in tear strength of 50%,y 10 3 2 13 Time required to achieve a reduction of elongation at breakf 50%, y 9% 14: 15 16 9% 10% vulcanisable composition is replaced by anequal weight of 2-(N-morpholinothio)-benzothiazole, the relativevariations of the scorching time asa function of the concentration ofN-nitroso-4,4-bis(Z-phenylisopropyl)diphenylamine remain on the sameorder of magnitude.

EXAMPLE 2 This example shows the influence of N-nitroso-4,4'- bis(2-phenylisopropyl)-diphenylamine on the scorching of a mixture based onbutadienestyrene copolymer contain-N-nitroso-4,4'-bis(2-phenylisopropyl)-diphenylamine (as indicatedbelow).

The excellent protection aiforded by the compound of the inventionrelative to the control material and also relative tonitrosodiphenylamine can clearly be seen.

EXAMPLE 4 A further advantage ofN-nitroso-4,4'-bis(2-phenylisopropyD-di-phenylamine compared toN-nitrosodiphenylamine, namely its much less pronounced marking oflacquers and paints, is demonstrated, in this example.

Mixtures prepared as in Example 1 are vulcanised for the optimum time at143 C. Samples of these vulcanised articles are brought into contactwith a 'white alkyd paint deposited on a metallic support. The time forthe appearance of a coloration on the paint is obsenved with each of thetwo diphenylamine derivatives.

Time for appearance of a c0loration in the paint Parts by weight HoursControl 90 N-nitr0s0-4, 4-bis (2-pheny1isopropyl) -d1phenyla- 0. 5 mine.1 75 N-nitrosodiphenylamine. f g;

EXAMPLE 5 The following composition, with the figures expressing partsby weight, is prepared with the aid of a mixer.

Cis-1,4-polybutadiene 100 Zinc oxide 5 Stearic acid 3 ISAF carbon black50 Pine tar 10 The following ingredients (parts by weight) are thenadded thereto on a roll mill Sulphur 1N-cyclohexylbenzothiazylsulphenamide 2 N-nitroso 4,4-bis(2-phenylisopropyl)-diphenylamine as indicated below.

After being left for 24 hours, the scorching time of the mixtures ismeasured on a consistometer of the Mooney type at 130 C. Furthermore theproperties of mixtures vulcanised at 153 C. are measured as a functionof the duration of vulcanisation. The results are collected in Table IV.

TABLE IV N -nitroso-4,4 -bis(2-phenylisopropyl) diphenylamine (parts byWeight) scorching time at 130 C. (in minutes). 26. 25 30. 25

Vulcanisation at 153 0.:

Duration (in minutes) 20 25 30 20 25 30 Tear strength (kg/0111. 129 140133 128 134 122 300% modulus (kgJcmfl) 63 63 62 57 59 60 Elongation atbreak percent 300 525 505 510 525 485 EXAMPLE 6 This example differsessentially from Example by the replacement of the polybutadiene bypolyisoprene.

The following mixture (in parts by weight) is prepared in a laboratoryinternal mixer Cis-1,4-polyisoprene 100 Zinc oxide 5 Stearic acid 3 Highabrasion furnace carbon black 50 Dutrex V (plasticiser obtained frompetroleum) 3 The following ingredients are added to this mixture on aroll mill:

Sulphur 2.5 N-cyclohexylbenzothiazylsulphenamide 1 N-nitroso 4,4bis(2-phenylisopropyl)-diphenylamine as indicated.

The results obtained are shown in Table V.

TABLE V N-nitro s04, 4'-bis (Z-phenylisopropyD-diphenylamine (parts byweight) Mooney scorching time, minutes:

At 120 C 32 35. 75

At 130 C 17. 75 20 Vulcanisation at 143 0.:

Duration (minutes) 17. 5 20 25 17. 5 20 25 Tear strength (kg./cm. 232255 232 254 259 234 300% modulus (kg/em!) 123 132 138 107 115 127Elongation at break (percent)- 480 505 445 555 545 475 6 EXAMPLE 7 Thisexample essentially diifers from Example 5 by the replacement of thepolybutadiene by a styreue-butadiene copolymer.

The following mixture (parts by weight) is prepared in a laboratoryinternal mixer Styrene-butadiene copolymer, type 1509 Zinc oxide 5Stearic acid 2 High abrasion furnace carbon black 50 Dutrex V 10 8 Thefollowing ingredients are added to the above mixture on a roll mill:

Sulphur 2 N-cyclohexylbenzothiazylsulphenamide 1 N-nitroso 4,4bis(2-phenylisopropyD-diphenylamine as indicated below.

The results obtained are shown in Table VI.

TABLE VI N -nitroso-4, 4-bis (2- phenylisopropyD- diphenylamine (partsby weight) Mooney scorching time (in minutes):

At C 46 55. 25 At C l4. 5 16.25

Vulcanisation at 153 0.:

Duration (minutes) 30 35 35 40 Tear strength (kg/em?) 184 162 182 300%modulus (kg/em?) 93 75 77 Elongation at break (percent 460 525 530UNITED STATES PATENTS 1,869,657 8/ 1932 Bowers 26045.9

2,035,698 3/ 1936 Fisher 26045.9

2,897,177 7/ 1959 Tung 26045.9

2,931,785 4/ 1960 Beaver et a1 260-453 3,384,613 5/1968 Parks 260-4533,505,225 4/ 1970 Wheeler 260-459 HOSEA E. TAYLOR, Primary Examiner US.Cl. X.R.

